Variable porosity fabric for aeronautical decelerator



Dec. 7, 1965 J. D. BOONE 3,222,016

VARIABLE POROS ITY FABRIC FOR AERONAUTICAL DECELERATOR Filed March 26, 1964 INVENTOR. JAY D. BOON E A TTOR/VE) United States Patent 3,222,016 VARIABLE POROSITY FABRIC FOR AERQNAU- TICAL DECELERATOR Jay D. Boone, Seeley, Calif., assignor to the United States of America as represented by the Secretary of the Navy Filed Mar. 26, 1964, Ser. No. 355,131 2 Claims. (Cl. 244145) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates in general to parachutes and more particularly to parachutes having a porosity or permeability which varies with the load so as to reduce opening shock and rate of descent.

Heretofore in the manufacture of parachutes it has been the aim to provide uniformity of yarn, weave and finish. It has also been an aim to provide a fabric of approximately the same strength and extension under load in both the warp and weft directions, and to this end, a uniform weave cloth has generally been used in the manufacture of parachutes. Although weight and bulk as well as strength are important factors in the performance of parachutes, the porosity of the parachute fabric is considered the most important factor and is the one which will be given greatest consideration in the present application.

A parachutes opening depends greatly on its canopy porosity. It is known that all fabrics become more porous with an increase in the pressure applied to their surfaces, and it has been determined that a linear relationship exists between porosity and pressure. The porous characteristics of a conventional ribbon mesh are similar to those of a fabric, while the effect of changing the material from which the ribbons are made has been found to be not so marked in ribbon parachutes as when normal woven fabrics are used.

The effect of tension in the warp and weft threads of the porosity of a fabric has been determined to vary with the material used. In the case of some fabrics, porosity increases with load, while with other fabrics porosity is scarcely affected by the load. In still other fabrics, porosity decreases as the load is increased. All cotton fabrics become more porous as the load is increased, while the porosity of nylon and spun silk fabrics have been determined to increase only slightly with load. The type of weave in a given conventional fabric seems to have no great effect on the change of porosity with change in load. In the case of many fabrics, an enlargement of the canopy can be observed as the load on the fabric is increased. It has been noted, however, that the difference in performance of an elastic fabric and another in which extension under load conditions is much less, that the extensibility of the fabric does not appear to have a very important part in changes in porosity. That is, it has heretofore been established that a fabric woven of all elastic fibers will not perform in a markedly different manner from a fabric woven of fibers having much less elasticity.

Prior attempts have been directed at making a parachute fabric having a variable porosity or permeability. These attempts have not been successful and therefore there is not yet available a parachute fabric which has the desirable characteristics of having a greater porosity during opening shock and a lessening porosity during the descent which follows. The present invention is directed toward providing such a fabric.

Accordingly, it is an object of the present invention to provide a fabric for use in construction of parachutes which will have a high permeability or porosity when 3,222,016 Patented Dec. 7, 1965 subjected to opening shock and a lower porosity during descent.

It is another object of the present invention to provide a parachute fabric in which the permeability will increase upon opening of the parachute and will progressively decrease as the speed of the descent decreases.

It is a still further object of the present invention to provide a parachute fabric having a desirable high opening shock porosity such that drogue parachutes may no longer be necessary in some high speed parachuting applications.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference characters refer to like parts in the several figures of the drawings.

FIG. 1 shows an enlarged portion of the fabric of one embodiment of the invention.

FIG. 2 illustrates the application of strips of material made of the fabric of the present invention in concentric relationship and assembled to form a parachute.

FIG. 3 illustrates an alternate assembling of strips of the material of the present invention to form a parachute.

FIG. 4 represents an alternate weave of material to form the fabric of the present invention.

FIG. 5 represents a further variation of weave in forming the fabric of the present invention.

The parachute fabric of the present invention achieves a variable permeability or porosity by providing changes in the geometry of the parachute without changing the structure of the cloth portions thereof. The variable permeability or porosity is attained by connecting conventional ribbon warps with wefts of a high modulous elastic material such as Spandex or Textured yarn. Upon the application of high loads such as encountered in opening shock the ribbon warps separate so as to permit a greater passage of air therebetween and thus reduce shock. Upon passing the high load occurrence, the ribbon warps are drawn closer together thus decreasing the permeability or porosity and thereby the rate of descent.

Referring to FIG. 1, there is shown one embodiment of the fabric of the present invention wherein ribbon warps 11 are shown extending in one direction in the fabric and are interspersed by warps 12 of standard yarn. Extending transverse to the warps 11 and 12 are wefts 13, also called fillers, which have a relatively high elasticity as well as a high percentage and high force recovery. The wefts 13 may be made of such material as high modulous Spandex or Textured yarns which are capable of being extended under high stress and have sulficient strength to retract when the stress is reduced. The patch 15 of material is taken from the areas 15 of the parachute canopies shown in FIGS. 2 and 3.

It will be appreciated that the change in permeability or porosity is occasioned by a change in spacing between the warp yarns, and therefore for diiferent applications such as supporting a human as against supporting an inert load a greater or lesser space between yarns will provide control of the amount of drag occasioned by the fabric. Since porosity has a considerable effect on the stability of a parachute in its descent, a large initial porosity may provide an increase in stability at the outset of a descent and therefore appreciably increase the stability of a given parachute. Heretofore, an increase in porosity has resulted in both a decrease in critical opening speed and an increase in descent speed. By providing a variable porosity, the critical opening speed is substantially unaltered and yet the speed of descent is lessened upon the elastic fibers contracting under a lesser load.

FIG. 2 shows a parachute canopy embodying the present invention in which lines of fabric are joined in concentric circles to form the canopy. The strips 17 are of the material of the present invention, and are joined or connected along main seams 18 by any suitable material possessing a sufiicient strength in relation to the weight of the fabric. The use of 3 lb. or 5 lb. thread of cotton or linen has been recommended for all parachutes in which the fabric strengthis less than 50 lb./in., with two rows of stitching considered adequate in either the main or cross seams. The fabric of the present invention is also applicable to the radially formed parachute canopy shown in FIG. 3, and in such a construction the gores or strips 19 would extend radially as would also the ribbon 11 of the fabric. The enlarged view in FIG. 1 of patches 15 in the canopies shown in FIGS. 2 and 3 depicts the direction of warp and weft threads or strands as they should be preferably arranged in the canopy configurations of FIGS. 2 and 3. That is, in the concentric strip configuration of FIG. 2 ribbons 11 preferably run parallel to main seams 18, while in the radial strip configuration of FIG. 3 ribbons 11 preferably run substantially parallel to main seams 20. In either of the configurations shown, and also in others within the concept of the invention but not shown, the strips 17 and 19 may be formed of panels having auxiliary seams, not shown, which would run at an angle to the main seams 18 and 20 and the peripheral hem of the parachute. The main seams may be constructed or made of the same material in any embodiment, and it will be appreciated that material having elasticity may be used for forming the seams as Well as non-elastic material.

The embodiments of FIGS. 4 and 5 present alternative means of weaving the fabric of the present invention, that of FIG. 4 having twice the number of warp yarns as the embodiment of FIG. 1, while that of FIG. 5 has twice the number of elastic weft strands as the embodiment of FIG. 1. With the number of warp lines doubled, or increased in other proportion to the embodiment of FIG. 1, the resulting fabric will have elasticity but to a lesser degree than the basic fabric. Conversely, with the number of elastic wefts doubled or otherwise increased the resulting fabric will have greater elasticity and greater porosity than the basic embodiment. It thus is apparent that the elasticity of the canopy may be varied by varying the ratio of yarn strands to weft strands, the change in elasticity being directly reflected in a change in porosity under load conditions.

The operation of the invention is substantially covered in the foregoing, however, it should be noted that the principle of variable porosity is based upon the circumstance that when loads are placed on the parachute canopy, as in opening shock, the ribbons will be selectively separated by extension of the wefts thereby increasing the area of spaces in the canopy and thus the volume of air that may escape therethrough. After the initial shock has occurred, the load impressed on the fabric is reduced and the extended weft yarns will contract somewhat depending upon their elasticity and the amount of reduction of load. This contraction reduces the area of spaces through which air escapes and also reduces the area of the canopy. Porosity is thereby leesened, thus slowing the rate of descent. Slowing of the rate of descent provides less pressure against the canopy and therefore permits further contraction of the elastic yarns until they have reached a selected length under selected load and speed of descent conditions.

The action upon initial shock being received by the canopy is to not only distend the canopy to its fullest geometrical pattern as occurs in a conventionalfabric, but also to enlarge it beyond the distended shape assumed by conventional fabric.

The fabric provided by the present invention enables drogue parachutes to be discontinued in applications where they have been used to reduce or eliminate damage to the parachute fabric from opening shock. The invention provides an automatic reaction between permeability and load which makes possible a reduction in parachute weight and bulk for a given application by reducing the strength needed to withstand opening shock as well as the size needed for a satisfactory speed of descent.

It will be recognized that many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. A parachute adapted to provide increased porosity on opening shock and decreasing porosity after the occurrence of opening shock comprising:

a canopy made of a plurality of gores joined together; each of said gores being formed of a material having interwoven warps at least some of which are of ribbon material and wefts of elastic material; and

said warps of ribbon material being substantially thicker than the warps of non-ribbon material;

so that opening shock will produce a greater force on said warps of ribbon material causing stretching of said wefts and consequent distention of said canopy and resulting in increased porosity of the canopy while the greater force thereon is maintained.

2. The device as defined in claim 1 wherein said wefts are radially disposed in said canopy and said warps are circumferentially disposed therein thus permitting maximum elongation of said wefts.

References Cited by the Examiner UNITED STATES PATENTS 2,173,976 9/1939 Moore 139-421 2,184,751 12/1939 Nathanson et al 139-421 2,959,385 11/1960 Buhler 244 3,032,072 5/1962 Weiner et al 244145 X MILTON BUCHLER, Primary Examiner.

FERGUS S. MIDDLETON, Examiner. 

1. A PARACHUTE ADAPTED TO PROVIDE INCREASED POROSITY ON OPENING SHOCK AND DECREASING POROSITY AFTER THE OCCURRENCE OF OPENING SHOCK COMPRISING: A CANOPY MADE OF A PLURALITY OF GORES JOINED TOGETHER; EACH OF SAID GORES BEING FORMED OF A MATERAIL HAVING INTERWOVEN WARPS AT LEAST SOME OF WHICH ARE OF RIBBON MATERIAL AND WEFTS OF ELASTIC MATERIAL; AND SAID WRAPS OF RIBBON MATERIAL BEING SUBSTANTIALLY THICKER THAN THE WARPS OF NON-RIBBON MATERIAL; SO THAT OPENING SHOCK WILL PRODUCE A GREATER FORCE ON SAID WRAPS OF RIBBON MATERIAL CAUSING STRETCHING OF SAID WEFTS AND CONSEQUENT DISTENTION OF SAID CANOPY 